The present invention provides low dielectric constant zinc oxide semiconductors, low dielectric constant zinc oxide insulators, and to fabrication methods thereof.
Since the introduction of the transistor, the semiconductor industry has seen an unprecedented rate of change in manufacturing productivity and device performance. The semiconductor industry is approaching a point at which conventional silicon dioxide dielectrics are inadequate for the function of insulating metal interconnects as the scale of integration and device speed increases. As integrated circuit (IC) dimensions continue to decrease, resistance-capacitance delay (RC delay), crosstalk noise, and power dissipation of the interconnect structure become limiting factors for ultra-large-scale integration of integrated circuits. Materials with low dielectric constant are desirable to replace silicon dioxide as interlevel dielectrics.
What is needed is an insulator with a lower dielectric constant (expressed as k value) than silicon dioxide. As used herein, a low-k dielectric is a dielectric material featuring a dielectric constant lower than that of SiO2. A dielectric is a solid that exhibits insulating properties. It typically has its upper most energy band completely empty which results in extremely low conductivity. The most common dielectrics in semiconductor technology are SiO2 and Si3N4. Low k dielectrics are used to insulate adjacent metal lines (interlayer dielectric, ILD) in advanced integrated circuits. The low k value reduces undesired capacitive coupling, and hence “cross talk” between lines.
Zinc oxide (ZnO), zinc sulfide (ZnS), and magnesium oxide (MgO) are wide band gap semiconductors with potential for use in electrically excited devices such as light emitting devices (LEDs), laser diodes (LDs), field effect transistors (FETs), photodetectors operating in the ultraviolet and at blue wavelengths of the visible spectrum, and other similar devices. Zinc oxide, zinc sulfide, and magnesium oxide are examples of group II-VI semiconductors compound.
As used herein, group II-VI semiconductor compounds include group II elements selected from zinc, cadmium, the alkaline earth metals such as beryllium, magnesium calcium, strontium, and barium, and mixtures thereof, and group VI elements selected from oxygen, sulfur, selenium, tellurium, and mixtures thereof. The group II-VI semiconductor compounds may be doped with one or more p-type dopant. Such p-type dopants include, but are not limited to, nitrogen, phosphorus, arsenic, antimony, bismuth, copper, chalcogenides of the foregoing, and mixtures thereof. The group II-VI semiconductor compounds may be doped with one or more n-type dopants. Such n-type dopants include, but are not limited to, ions of Al, Ga, B, H, Yb and other rare earth elements, Y, Sc, and mixtures thereof.
N-type zinc oxide semiconductor materials are known and relatively easy to prepare, such as ZnO doped with aluminum, gallium, or other known n-type dopants. P-type zinc oxide semiconductor materials are theoretically possible, but have been difficult to prepare. D. C. Look et al., “The Future of ZnO Light Emitters,” Phys. Stat. Sol., 2004, summarize data on p-type ZnO samples reported in the literature. The best reported ZnO samples have resistivity values of 0.5 ohm·cm (N/Ga dopants) and 0.6 ohm·cm (P dopant). Many of the reported p-type zinc oxide samples tend to be light, heat, oxygen, and moisture sensitive. Some convert to n-type material over time. Their stability has been questioned and instability has been observed. Some of the more-stable p-type zinc oxide materials reported in the literature are prepared using complex and expensive fabrication processes, such as molecular beam epitaxy. No commercially viable p-type zinc oxide semiconductor materials are currently known.
Without being bound by theory, it is presently believed one possible explanation for the lack of p-type zinc oxide materials is because high temperature diffusion processes or other fabrication methods inhibit formation of desirable p-type zinc oxide compounds. In particular, it is presently believed that high temperature fabrication of p-type zinc oxide transforms the zinc oxide from a semiconductor to an insulator.